Sumitomo fought off competition from China Development Bank Corp to buy Dublin-based RBS Aviation Corp for about $7.3bn in what will be seen as a major success for the state-backed lender RBS as it attempts to become a more UK-focused business.

RBS Aviation is the world's fifth-largest aircraft leasing business by the value of its fleet and manages or has on order 466 aircraft.

The unit leases aircraft to airlines in 24 countries and has offices across the world, including in New York, Hong Kong and Tokyo.

Buying the RBS business will see Sumitomo, which operates its own much smaller aircraft leasing business, become the world's fourth-biggest aviation leasing company.

About one-fifth of the purchase price will go towards buying RBS Aviation's equity while the rest will go towards taking on its debt.

"The deal is expected to complete before the end of the third quarter, and will be seen as a major part of RBS's attempt to restructure its business," said Bruce Van Saun, RBS finance director, on Monday evening.

"Reaching agreement on a deal of this scale in such a volatile market is a significant success for our non-core division."

RBS Aviation was originally put up for sale two years ago, however the lender abandoned an early attempt to sell the business after aircraft prices plummeted in 2009 in the immediate aftermath of the financial crisis.

RBS has set up the non-core division to manage the sell-down of businesses that will not form part of its ongoing operations.

George Osborne, the Chancellor, has endorsed RBS's plans to continue shrinking its business and last month said the bank must become smaller and more focused on the UK banking market.

Next month, RBS will announce its full-year results for 2011, which are expected to show the bank made a small profit. Stephen Hester, chief executive, will announce further details of the bank's restructuring at the results presentation on February 23.